The following description is provided to assist the understanding of the reader. None of the information provided or references cited is admitted to be prior art to the present technology.
The vitreous humor is an approximately spherical transparent gel and has a weight of approximately 4 g and a volume of about 4 mL, occupying a substantial volume in the eye. It has a significant content of water, about 98%. The vitreous does not adhere to the retina, except at three places: all around the anterior border of the retina, at the macula, and at the optic nerve disc. The vitreous is hydrophilic in nature with a water contact angle of 25-27. Light transmitted by the vitreous humor is in the range of 85-95% between the wavelengths 400-700 nm allowing maximum light to reach the retina resulting in clear vision. Some of the ailments that cause posterior segment disorders are spontaneous-retinal detachment, degeneration, age related macular disorder (ARMD), diabetic retinopathy, trauma-accidental or surgical, infection-toxocara/syphilis, tumors. Infectious conditions may respond to drug therapy, while tumors usually require surgery and may involve the loss of the eye. However, in many of these conditions, the direct cause of blindness is either neovascularization or retinal detachment. The various forms of retinal detachment are rhegmatogenous retinal detachment, tractional contractile membranes formed upon the retina, leading to the neural retina being pulled off the retinal pigment epithelium; exudative, where a build-up of fluid in the subretinal space beneath the neural retina is caused by disruption of the choroid leads to the elevation and detachment of the retina from the retinal pigment epithelium. In the case of ARMD, there is neovascularization which is subretinal, while in diabetic retinopathy, the neovascularization is intravitreal leading to vitreous hemorrhage. The treatments available for these pathologies are limited.
Vitreoretinal diseases are a major cause of blindness worldwide. These include retinal detachment, diabetic retinopathy and age related degeneration of the vitreous. Other disorders that cause retinal detachment include severe ocular infections, inflammations, and traumatic injuries to the eye. Age-related macular degeneration and macular holes are also conditions that require retinal support materials and drug therapy. All of these conditions require the damaged vitreous humor to be removed and replaced either partially or totally by artificial substitutes. Vitreous replacement is also required during posterior ocular surgeries both during and after the surgical procedures. Further, cataract formation or acceleration can occur after intraocular surgery, especially following vitrectomy, a surgical technique for removing the vitreous used in the treatment of disorders that affect the posterior segment of the eye. This is associated with an accumulation of oxidants in the eye due to loss of the oxidant scavenging function of the natural vitreous.
Vitreoretinal surgery is employed in the later stages of diabetic retinopathy where vitrectomy and vitreous substitution are used in addition to laser treatment, and may be of use in the treatment of ARMD. In the treatment of rhegmatogenous retinal detachment, except for large tears, pneumatic retinopexy or scleral buckling is performed with the purpose of sealing the tear. Tamponade agents such as balanced salt solutions or silicone oil may be used to keep the retina in place (Colthurst et al., 2000). Sodium hyaluronate, a component of the vitreous, was tried as a substitute without much success (Delinger et al., 1980). Silicone oil is hydrophobic and has many side effects like emulsification, cataract formation, keratopathy and optic nerve atrophy (Giovanni et al., 1998).